fs/attr.c

   1 /*
   2  *  linux/fs/attr.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  *  changes by Thomas Schoebel-Theuer
   6  */
   7
   8 #include <linux/export.h>
   9 #include <linux/time.h>
  10 #include <linux/mm.h>
  11 #include <linux/string.h>
  12 #include <linux/sched/signal.h>
  13 #include <linux/capability.h>
  14 #include <linux/fsnotify.h>
  15 #include <linux/fcntl.h>
  16 #include <linux/security.h>
  17 #include <linux/evm.h>
  18 #include <linux/ima.h>
  19
  20 static bool chown_ok(const struct inode *inode, kuid_t uid)
  21 {
  22         if (uid_eq(current_fsuid(), inode->i_uid) &&
  23             uid_eq(uid, inode->i_uid))
  24                 return true;
  25         if (capable_wrt_inode_uidgid(inode, CAP_CHOWN))
  26                 return true;
  27         if (ns_capable(inode->i_sb->s_user_ns, CAP_CHOWN))
  28                 return true;
  29         return false;
  30 }
  31
  32 static bool chgrp_ok(const struct inode *inode, kgid_t gid)
  33 {
  34         if (uid_eq(current_fsuid(), inode->i_uid) &&
  35             (in_group_p(gid) || gid_eq(gid, inode->i_gid)))
  36                 return true;
  37         if (capable_wrt_inode_uidgid(inode, CAP_CHOWN))
  38                 return true;
  39         if (ns_capable(inode->i_sb->s_user_ns, CAP_CHOWN))
  40                 return true;
  41         return false;
  42 }
  43
  44 /**
  45  * setattr_prepare - check if attribute changes to a dentry are allowed
  46  * @dentry:     dentry to check
  47  * @attr:       attributes to change
  48  *
  49  * Check if we are allowed to change the attributes contained in @attr
  50  * in the given dentry.  This includes the normal unix access permission
  51  * checks, as well as checks for rlimits and others. The function also clears
  52  * SGID bit from mode if user is not allowed to set it. Also file capabilities
  53  * and IMA extended attributes are cleared if ATTR_KILL_PRIV is set.
  54  *
  55  * Should be called as the first thing in ->setattr implementations,
  56  * possibly after taking additional locks.
  57  */
  58 int setattr_prepare(struct dentry *dentry, struct iattr *attr)
  59 {
  60         struct inode *inode = d_inode(dentry);
  61         unsigned int ia_valid = attr->ia_valid;
  62
  63         /*
  64          * First check size constraints.  These can't be overriden using
  65          * ATTR_FORCE.
  66          */
  67         if (ia_valid & ATTR_SIZE) {
  68                 int error = inode_newsize_ok(inode, attr->ia_size);
  69                 if (error)
  70                         return error;
  71         }
  72
  73         /* If force is set do it anyway. */
  74         if (ia_valid & ATTR_FORCE)
  75                 goto kill_priv;
  76
  77         /* Make sure a caller can chown. */
  78         if ((ia_valid & ATTR_UID) && !chown_ok(inode, attr->ia_uid))
  79                 return -EPERM;
  80
  81         /* Make sure caller can chgrp. */
  82         if ((ia_valid & ATTR_GID) && !chgrp_ok(inode, attr->ia_gid))
  83                 return -EPERM;
  84
  85         /* Make sure a caller can chmod. */
  86         if (ia_valid & ATTR_MODE) {
  87                 if (!inode_owner_or_capable(inode))
  88                         return -EPERM;
  89                 /* Also check the setgid bit! */
  90                 if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
  91                                 inode->i_gid) &&
  92                     !capable_wrt_inode_uidgid(inode, CAP_FSETID))
  93                         attr->ia_mode &= ~S_ISGID;
  94         }
  95
  96         /* Check for setting the inode time. */
  97         if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) {
  98                 if (!inode_owner_or_capable(inode))
  99                         return -EPERM;
 100         }
 101
 102 kill_priv:
 103         /* User has permission for the change */
 104         if (ia_valid & ATTR_KILL_PRIV) {
 105                 int error;
 106
 107                 error = security_inode_killpriv(dentry);
 108                 if (error)
 109                         return error;
 110         }
 111
 112         return 0;
 113 }
 114 EXPORT_SYMBOL(setattr_prepare);
 115
 116 /**
 117  * inode_newsize_ok - may this inode be truncated to a given size
 118  * @inode:      the inode to be truncated
 119  * @offset:     the new size to assign to the inode
 120  * @Returns:    0 on success, -ve errno on failure
 121  *
 122  * inode_newsize_ok must be called with i_mutex held.
 123  *
 124  * inode_newsize_ok will check filesystem limits and ulimits to check that the
 125  * new inode size is within limits. inode_newsize_ok will also send SIGXFSZ
 126  * when necessary. Caller must not proceed with inode size change if failure is
 127  * returned. @inode must be a file (not directory), with appropriate
 128  * permissions to allow truncate (inode_newsize_ok does NOT check these
 129  * conditions).
 130  */
 131 int inode_newsize_ok(const struct inode *inode, loff_t offset)
 132 {
 133         if (inode->i_size < offset) {
 134                 unsigned long limit;
 135
 136                 limit = rlimit(RLIMIT_FSIZE);
 137                 if (limit != RLIM_INFINITY && offset > limit)
 138                         goto out_sig;
 139                 if (offset > inode->i_sb->s_maxbytes)
 140                         goto out_big;
 141         } else {
 142                 /*
 143                  * truncation of in-use swapfiles is disallowed - it would
 144                  * cause subsequent swapout to scribble on the now-freed
 145                  * blocks.
 146                  */
 147                 if (IS_SWAPFILE(inode))
 148                         return -ETXTBSY;
 149         }
 150
 151         return 0;
 152 out_sig:
 153         send_sig(SIGXFSZ, current, 0);
 154 out_big:
 155         return -EFBIG;
 156 }
 157 EXPORT_SYMBOL(inode_newsize_ok);
 158
 159 /**
 160  * setattr_copy - copy simple metadata updates into the generic inode
 161  * @inode:      the inode to be updated
 162  * @attr:       the new attributes
 163  *
 164  * setattr_copy must be called with i_mutex held.
 165  *
 166  * setattr_copy updates the inode's metadata with that specified
 167  * in attr. Noticeably missing is inode size update, which is more complex
 168  * as it requires pagecache updates.
 169  *
 170  * The inode is not marked as dirty after this operation. The rationale is
 171  * that for "simple" filesystems, the struct inode is the inode storage.
 172  * The caller is free to mark the inode dirty afterwards if needed.
 173  */
 174 void setattr_copy(struct inode *inode, const struct iattr *attr)
 175 {
 176         unsigned int ia_valid = attr->ia_valid;
 177
 178         if (ia_valid & ATTR_UID)
 179                 inode->i_uid = attr->ia_uid;
 180         if (ia_valid & ATTR_GID)
 181                 inode->i_gid = attr->ia_gid;
 182         if (ia_valid & ATTR_ATIME)
 183                 inode->i_atime = timespec_trunc(attr->ia_atime,
 184                                                 inode->i_sb->s_time_gran);
 185         if (ia_valid & ATTR_MTIME)
 186                 inode->i_mtime = timespec_trunc(attr->ia_mtime,
 187                                                 inode->i_sb->s_time_gran);
 188         if (ia_valid & ATTR_CTIME)
 189                 inode->i_ctime = timespec_trunc(attr->ia_ctime,
 190                                                 inode->i_sb->s_time_gran);
 191         if (ia_valid & ATTR_MODE) {
 192                 umode_t mode = attr->ia_mode;
 193
 194                 if (!in_group_p(inode->i_gid) &&
 195                     !capable_wrt_inode_uidgid(inode, CAP_FSETID))
 196                         mode &= ~S_ISGID;
 197                 inode->i_mode = mode;
 198         }
 199 }
 200 EXPORT_SYMBOL(setattr_copy);
 201
 202 /**
 203  * notify_change - modify attributes of a filesytem object
 204  * @dentry:     object affected
 205  * @iattr:      new attributes
 206  * @delegated_inode: returns inode, if the inode is delegated
 207  *
 208  * The caller must hold the i_mutex on the affected object.
 209  *
 210  * If notify_change discovers a delegation in need of breaking,
 211  * it will return -EWOULDBLOCK and return a reference to the inode in
 212  * delegated_inode.  The caller should then break the delegation and
 213  * retry.  Because breaking a delegation may take a long time, the
 214  * caller should drop the i_mutex before doing so.
 215  *
 216  * Alternatively, a caller may pass NULL for delegated_inode.  This may
 217  * be appropriate for callers that expect the underlying filesystem not
 218  * to be NFS exported.  Also, passing NULL is fine for callers holding
 219  * the file open for write, as there can be no conflicting delegation in
 220  * that case.
 221  */
 222 int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **delegated_inode)
 223 {
 224         struct inode *inode = dentry->d_inode;
 225         umode_t mode = inode->i_mode;
 226         int error;
 227         struct timespec now;
 228         unsigned int ia_valid = attr->ia_valid;
 229
 230         WARN_ON_ONCE(!inode_is_locked(inode));
 231
 232         if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
 233                 if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
 234                         return -EPERM;
 235         }
 236
 237         /*
 238          * If utimes(2) and friends are called with times == NULL (or both
 239          * times are UTIME_NOW), then we need to check for write permission
 240          */
 241         if (ia_valid & ATTR_TOUCH) {
 242                 if (IS_IMMUTABLE(inode))
 243                         return -EPERM;
 244
 245                 if (!inode_owner_or_capable(inode)) {
 246                         error = inode_permission(inode, MAY_WRITE);
 247                         if (error)
 248                                 return error;
 249                 }
 250         }
 251
 252         if ((ia_valid & ATTR_MODE)) {
 253                 umode_t amode = attr->ia_mode;
 254                 /* Flag setting protected by i_mutex */
 255                 if (is_sxid(amode))
 256                         inode->i_flags &= ~S_NOSEC;
 257         }
 258
 259         now = current_time(inode);
 260
 261         attr->ia_ctime = now;
 262         if (!(ia_valid & ATTR_ATIME_SET))
 263                 attr->ia_atime = now;
 264         if (!(ia_valid & ATTR_MTIME_SET))
 265                 attr->ia_mtime = now;
 266         if (ia_valid & ATTR_KILL_PRIV) {
 267                 error = security_inode_need_killpriv(dentry);
 268                 if (error < 0)
 269                         return error;
 270                 if (error == 0)
 271                         ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV;
 272         }
 273
 274         /*
 275          * We now pass ATTR_KILL_S*ID to the lower level setattr function so
 276          * that the function has the ability to reinterpret a mode change
 277          * that's due to these bits. This adds an implicit restriction that
 278          * no function will ever call notify_change with both ATTR_MODE and
 279          * ATTR_KILL_S*ID set.
 280          */
 281         if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) &&
 282             (ia_valid & ATTR_MODE))
 283                 BUG();
 284
 285         if (ia_valid & ATTR_KILL_SUID) {
 286                 if (mode & S_ISUID) {
 287                         ia_valid = attr->ia_valid |= ATTR_MODE;
 288                         attr->ia_mode = (inode->i_mode & ~S_ISUID);
 289                 }
 290         }
 291         if (ia_valid & ATTR_KILL_SGID) {
 292                 if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
 293                         if (!(ia_valid & ATTR_MODE)) {
 294                                 ia_valid = attr->ia_valid |= ATTR_MODE;
 295                                 attr->ia_mode = inode->i_mode;
 296                         }
 297                         attr->ia_mode &= ~S_ISGID;
 298                 }
 299         }
 300         if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID)))
 301                 return 0;
 302
 303         /*
 304          * Verify that uid/gid changes are valid in the target
 305          * namespace of the superblock.
 306          */
 307         if (ia_valid & ATTR_UID &&
 308             !kuid_has_mapping(inode->i_sb->s_user_ns, attr->ia_uid))
 309                 return -EOVERFLOW;
 310         if (ia_valid & ATTR_GID &&
 311             !kgid_has_mapping(inode->i_sb->s_user_ns, attr->ia_gid))
 312                 return -EOVERFLOW;
 313
 314         /* Don't allow modifications of files with invalid uids or
 315          * gids unless those uids & gids are being made valid.
 316          */
 317         if (!(ia_valid & ATTR_UID) && !uid_valid(inode->i_uid))
 318                 return -EOVERFLOW;
 319         if (!(ia_valid & ATTR_GID) && !gid_valid(inode->i_gid))
 320                 return -EOVERFLOW;
 321
 322         error = security_inode_setattr(dentry, attr);
 323         if (error)
 324                 return error;
 325         error = try_break_deleg(inode, delegated_inode);
 326         if (error)
 327                 return error;
 328
 329         if (inode->i_op->setattr)
 330                 error = inode->i_op->setattr(dentry, attr);
 331         else
 332                 error = simple_setattr(dentry, attr);
 333
 334         if (!error) {
 335                 fsnotify_change(dentry, ia_valid);
 336                 ima_inode_post_setattr(dentry);
 337                 evm_inode_post_setattr(dentry, ia_valid);
 338         }
 339
 340         return error;
 341 }
 342 EXPORT_SYMBOL(notify_change);